Response To Salt Stress In Rhizosphere Of Sea Rice 86 And Isolation And Identification Of Salt-Tolerant Strains

Sea Rice 86(SR86)is a special rice germplasm resource.Because of its strong tolerance to salt and submergence,it has high scientific research and application value.However,there are relatively few reports on the mechanism of salt tolerance of SR86,especially on the role of rhizosphere microorganisms in the process of salt tolerance of SR86.In this paper,SR86 was selected as the research object to systematically clarify the effects of salt stress on rhizosphere microorganisms and their metabolites through the analysis of rhizosphere microbial diversity,rhizosphere metabolome and bioinformatics,and to isolate rhizosphere microbial strains that can promote salt tolerance of SR86 plants based on pure culture technology.In this study,SR86 seedlings at three-leaf and one-heart stage were used as the research materials.Firstly,diluted seawater and farmland soil were selected to establish a stable salt stress condition to determine its salt tolerance range.Then,SR86 seedlings were transplanted to 0(non-salt stress),0.2%and 0.4%salinity treatments,and the rhizosphere soil and non-rhizosphere soil of SR86 seedlings were collected after 15 days of cultivation.On the one hand,high-throughput sequencing and bioinformatics analysis were used to determine the effects of salt stress on SR86 rhizosphere microbial diversity and related metabolites.Furthermore,co-occurrence network analysis and microbial diversity-metabolome association analysis were used to obtain information on key rhizosphere microbial species and related metabolites that may be involved in promoting salt tolerance of SR86 plants.On the other hand,on the basis of preliminary elucidation of SR86rhizosphere microorganisms promoting plant salt tolerance,rhizosphere microbial strains that can promote SR86 salt tolerance were isolated,and the mechanism of the strains promoting salt tolerance was studied.The results showed that the survival rate of SR86 seedlings was above 96.7%when the salinity was less than or equal to 0.4%(w/v),but the survival rate decreased rapidly with the increase of salinity,and the growth and development of SR86 seedlings also showed stress response.Significant differences in microbial diversity occurred under salt stress,and salt stress increased microbial diversity in the rhizosphere.The metabolites in the rhizosphere soil of SR86 plants with different salinities are highly complex mixtures and have significant differences,and the differentially expressed rhizosphere metabolites are mainly lipids and their derivatives.Subsequent analysis found that rhizosphere microorganisms showed significant modularity under salt stress,and 15 core microbial species were identified,speculating that specific metabolites may recruit specific key groups or specific key groups may produce specific products to promote plant salt tolerance.In addition,four strains of rhizosphere microorganisms were isolated in this study,which could improve the salt tolerance of plants.The results were as follows:(1)The survival rate of SR86 was above 96.7%when the salinity was less than 0.4%,and decreased to 71.7%when the salinity increased to0.5%;At the same time,with the increase of salinity,the plant showed different degrees of salt stress response.(2)Salt stress can significantly change the diversity of rhizosphere bacteria and the composition of rhizosphere metabolites,and several rhizosphere bacterial groups may participate in the response of SR86 to salt stress as key groups;further,through bioinformatics analysis,the characteristics of SR86 rhizosphere microbial network under salt stress were determined,and 15 key microbial nodes were identified;The lipid and its derivatives in the metabolites form a membrane protective layer,which can protect SR86 from the effects of salt stress by binding Na~+and block Cl~-outside root cells under the action of anion channel blockers(IAA-94).(3)Four kinds of growth-promoting rhizobacteria were obtained,which could enhance the salt tolerance of Sea Rice 86.Among them,the strain RL-WG62 of Rossellomorea vietnamensis had the best effect on promoting salt tolerance.After inoculation with RL-WG62,the proline and MDA contents of plants under salt stress were significantly reduced,and the chlorophyll content and dry weight of plants under salt stress and non-salt stress were significantly increased.The results showed that RL-WG62 was not only a plant growth-promoting bacterium,but also a plant growth-promoting bacterium.